Method for producing nutritionally dense freeze dried food bars

ABSTRACT

A method of producing a nutritionally dense, freeze dried food item usuallyn bar form in which uncooked food ingredients are mixed together and then cooked until about 40% to about 60% of the water content is removed by evaporation. Then the partially dried mixture is formed into the desired shape, then frozen and dehydrated to a moisture level which would produce a shelf-stable product. The freeze dried bars are packaged in impermeable containers. Food bars prepared by this method rehydrate faster and to a greater extent than food bars prepared by processes incorporating a compression step.

The invention described herein may be manufactured, used, and licensedby or for the Government for governmental purposes without the paymentto us of any royalty thereon.

BACKGROUND OF THE INVENTION

This invention relates to a method of producing freeze-vacuum-dehydratedparticulate foods, such as vegetables and meats without resorting tocompaction, such that the dehydrated foods will have bulk densitieswhich nearly approach the bulk densities of compacted foods. These foodsreadily rehydrate to substantially the same distinct particulate statesin which they existed prior to freeze dehydration.

Freeze drying of foods is a well-known method for preserving foods sothat they can be stored at room temperature or even higher temperaturesfor long periods of time, provided they are maintained at very lowmoisture levels during such storage. When properly prepared and stored,such foods may be rehydrated at the time it is desired to consume them,the reconstituted foods being of quality approaching that of freshlyprepared foods of the same types.

In recent years, the military forces have found it to be highlydesirable to utilize freeze dried foods in compact form so that thefoods will occupy appreciably less space in submarines, in aircraft andalso when carried on the person. Compact foods are generally formed intocylindrical or rectangular shaped bars which are of a convenient form tobe stored and carried.

Various techniques have been used to reduce the volumes and increase thedensities of dehydrated foods without destroying the ability to returnto substantially the conditions they were in prior to dehydration. Thetechnology for forming freeze dried food bars by compression is complexand costly, requiring considerable handling of the product with acommensurate loss in quality. The techniques heretofore employedrequired two freeze drying steps and a plasticization step.

One of the methods of producing compacted freeze-dried foods is inaccordance with the teachings of Ishler et al, U.S. Pat. No. 3,385,715,whereby a food is first freeze-dried to a low moisture level, such asabout 1.1% to about 2.2%. Then the freeze dried food is sprayed withenough water to raise its average moisture content to from about 5% toabout 13% so that, when compaction of the freeze-dried food is carriedout, the food will not shatter, but will flow while maintaining itscellular structure and the particles of food will adhere to each otherwhen compacted. The added moisture serves as a plasticizer whichprevents pulverization of the dried food during mechanical compaction.In order for plasticization to have the desired effect, the foodparticles must be sprayed with water or an aqueous solution of a gum orthe like and then to be permitted to stand long enough for the water tosubstantially equilibrate throughout the food particles. Thisequilibration process may take several hours to permit uniformdistribution of the added water. After compaction is carried out, thecompacted food is usually freeze-vacuum dehydrated to a moisture levelsufficiently low to maintain good quality upon storage. This, of course,means that a substantial amount of freeze drying, an expensive processin itself, has to be repeated to remove the water added during theplasticization step. Futhermore, the slowness of the equilibration makesit virtually necessary for the dehydration and compaction process to becarried out in stages rather than in a continuous manner, as would bedesirable, resulting in higher production costs and lower productquality.

Various approaches have been made to avoid the above-mentionedrepetition of freeze-drying in the production of nutritionally densefood bars. One such approach involves stopping the initial freeze-dryingof the food particles to a moisture level of from 5 to about 13% andthen compacting the partially freeze-dried food. However, as is wellknown in the food freeze drying art, the cores of the food particlesbeing freeze vacuum dehydrated remain frozen until most of the moisturethat is removed from the food has sublimed and the water vapor formedthereby has migrated through the outer portions of the food particlesunder the influence of the vacuum. Thus, if thefreeze-vacuum-dehydration is stopped at 5-13 percent moisture content asdisclosed in the Ishler et al patent, the outer portions of theparticles of food are extremely dry while the cores contain essentiallytheir original concentrations of water as ice. If such food particlesare then compacted without permitting equilibration to occur, theextremely dry outer portions of the particles shatter and the compactedproduct has very poor properties. In such a case, it is impossible torestore the original particle sizes and shapes upon rehydration. Onesolution to this problem is to hold the particles of partiallyfreeze-dried food in closed containers at temperatures have 0° C. topermit equilibration of the moisture from the frozen cores throughoutthe particles of food. Such equilibration, however, proceeds veryslowly, and the larger the food particles, the more slowly equilibrationoccurs.

U.S. Pat. No. 4,096,283 disclosed a method of speeding up theequilibration process described above through the use of microwaveenergy to distribute the moisture through the food. However, thisprocess retains the disadvantages inherent in two freeze vacuumdehydration steps with the additional handling of the food required. InU.S. Pat. No. 3,950,560 the disadvantages of two freeze drying stepswere avoided by predrying (without freezing) a vegetable in morsel formto a moisture content from about 7 percent to about 18 percent byweight, compressing the predried, vegetable morsels to form a compacted,vegetable mass and then redrying the compacted vegetable mass to amoisture content of less that 5 percent by weight. Prior efforts toproduce a satisfactory nutritionally-dense, freeze-dehydrated foodproduct share several undesirable characteristics. Compressed food barsrehydrate slowly. Frequently, warm or hot water is required to rehydratewithin a reasonable period of time. Furthermore, those processes whichrequire multiple applications of freeze-vacuum-dehydration, as opposedto a single application, cause the food to be exposed to air for longerperiods of time with an increase in deterioration due to oxidativerancidity.

It is an object of this invention to provide an improved method ofproducing nutritionally dense freeze dried food bars so that uponrehydration the foods will be restored to substantially the samedistinct particulate form in which they existed prior to dehydration ofthe foods and so that the reconstituted foods will be of high qualityand as closely comparable as possible to the original raw or cookedfoods from which the freeze-dried particulate foods are prepared.

Other objects and advantages will become apparent from the followingdescription of the invention.

SUMMARY OF THE INVENTION

Production of nutritionally-dense, freeze-dried, food bars according tothis invention is accomplished by first preparing a mixture ofparticulate food ingredients which are predried during a cooking processto a moisture level about 40 percent to about 60 percent less butpreferably about 45 percent to about 55 percent than the moisture levelprior to predrying. The predrying will occur as direct evaporationduring the cooking process. The partially dried product is formed intoany desired shape by packing into an appropriate container. The productis then frozen and while frozen is sliced into the desired size productwhich is placed in a freeze dryer and dehydrated to about 2.0 percentmoisture. After dehyration the dried product is enclosed in a packagewhich is impermeable to air and moisture. The dehydrated food barsproduced by this invention have bulk densities which nearly approach thebulk densities of similar but compressed food bars and rehydrate fasterand to a greater extent than food bars prepared by a processincorporating a compression step.

DESCRIPTION OF THE INVENTION

This invention produces nutritionally-dense dehydrated food bars withoutcompression. It has been found that partial predrying prior tofreeze-drying allows the production of a food bar having nearly similardensity to that produced by compression such as described in U.S. PatentNo. 3,385,715, but with the capability of rehydrating more quickly andmore thoroughly than the freeze-dried compressed item. This improvedproduct occurs for several reasons. During the cooking of the mixture ofingredients to be incorporated in the food bar, about 40 percent to 60percent of the water content is allowed to exaporate. The cooking isdone in a conventional or vacuum steam jacketed kettle. The amount ofwater removed at this stage will determine the ultimate density,compactness, cohesion and rate and extent of rehydration of the endproduct. If too much water is removed at this stage, then the productbecomes too dense and rehydration becomes difficult. If on the otherhand, not enough water is removed, then the finished product will not bedense enough. When the correct amount of water is removed during thecooking stage, the volume of food material diminishes with acorresponding increase in density. After the cooked and partiallydehydrated food bars have been packed or formed into the desired shape,there remain no visible voids or air pockets. There does, however,remain about 45 percent to 55 percent water which, following freezing,becomes randomly distributed ice crystals throughout the bars. Thesublimation of these ice crystals during freeze dehydration results inthe creation of an open i.e. porous structure with a large surface areafor rapid penetration and imbibition of water during the rehydrationstep. With the existence of this open structure there is a greateropportunity for and less resistance to penetration and uptake of waterduring rehydration than in compressed foods where the open structureresulting from freeze dehydration is largely destroyed by mechanicalcompaction.

The dehydrated food bars typically had a density of about 0.60grams/cubic centimeter and almost always the density was in the range of0.40 to 0.70g/cc. These densities were about 80% to about 110% ofcompressed, dehyrated food bars. The compressed food bars had beencompressed at pressures above 300 pounds per square inch while with theinvention described herein there is no such compression. The pressuresused in forming compressed food bars have typically been described asbeing in the range of 1500 pounds per square inch.

The predried foods can be packed or molded by being stuffed into sausagecasings of the desired circumference and frozen to obtain cylindricalfood logs. Other geometrical shapes may be obtained by restraining thefood by metal, plastic or wood compession plates, boxes, mols, cages orspring loaded screens or by other means prior to freezing. The frozenshaped food bar may then be cut into individual portions. It is to beunderstood that whenever a "food bar" is referred to this is not to belimited to a rectangular shape but may be of any shape desired.Alternatively, the cooked, partially dried product may be dispensed intoindividual molds of the desired shape or machine formed into the desiredshape. Food bars may be formed in any desired shape that is appropriatefor freeze-dehydration. For example, bars having dimensions of 1×3×0.5inches have been found to be suitable from the standpoint of relativeease of freeze dehydration and packaging. The molded or formed productis then solidly frozen prior to freeze drying. The freeze-vacuumdehydration of the foods may be carried out by any conventional processfor freeze vacuum dehydrating food products. The food bar is dehydratedto a moisture content of from about 1% to about 5% and preferably, forlong-term storage, not more than 2%, to provide stability of the foodwhen it is packaged in a moisture and gas impermeable container. Thefinal drying may also be done by vacuum oven drying without freezing.The packaging material which is impermeable to moisture and preferablyimpermeable to oxygen may be a flexible package made of a laminate whichusually comprises one layer which is heat-sealable and is the innermostlayer of the package, such as polyethylene and an outermost layer of amaterial which is strong and resistant to most common types of damage,such as polyethylene terephthalate. Aluminum foil, an effective moistureand gas barrier, is sandwiched between the inner heat-sealablepolyethylene layer and the strong outer layer of polyethyleneterephthalate.

The following specific examples of formulations of nutritionally densefood items are only several of the examples of formulations which may bereadily made in accordance with the above described principles of theinvention. A wide variety of meats and vegetables may be used in foodbars. Fruits and grains could also be incorporated in formulations. Itwill be understood, of course, that the above-mentioned and otheradvantages of this invention may also be accomplished by suitablevariations in the detailed method steps, about to be set forth below,which are intended to be for illustrative purposes, and not for limitingthe scope of the invention. All of the percentages used are by weight.

Example 1

A beef stew food bar is prepared by mixing the following ingredients ofthe percentage levels noted:

    ______________________________________                                        Ingredient         %                                                          ______________________________________                                        Ground Beef        49.00                                                      Dehydrated diced onion                                                                           1.00                                                       Onion powder       0.65                                                       Salt               1.00                                                       Ground black pepper                                                                              0.08                                                       Garlic powder      0.03                                                       Dehydrated beef stock                                                                            1.50                                                       Ground paprika     0.10                                                       Ground celery seed 0.03                                                       Granular lecithin  0.22                                                       Caramel color      0.10                                                       Ground bay leaf    0.02                                                       Ground all spice   0.02                                                       ______________________________________                                    

To the above mixed ingredients is added a mixture consisting of:

    ______________________________________                                        Ingredient (Cont.)    %                                                       ______________________________________                                        Corn starch, modified 2.00                                                    Microcrystalline cellulose                                                                          0.75                                                    Gum arabic            2.00                                                    ______________________________________                                    

A vegetable mixture consisting of the following mixture of peas, carrotsand potatoes is added:

    ______________________________________                                        Frozen slit peas      5.50                                                    Frozen diced carrots  14.00                                                   Dehydro-frozen diced potatoes                                                                       22.00                                                   ______________________________________                                    

The potatoes used have been partially freeze dried. Before being addedto the formulation, the potatoes are rehydrated to their normal waterlevel. Blanched potatoes may be substituted. The mixture is cooked in asteam kettle until the moisture content is preferably reduced about 45%to about 55% below the moisture level before cooking. The cooking is forabout 30 minutes. The partially dried mixture is then molded by stuffinginto sausage casings. After being molded the formed food bar is frozensolid at -40° F. and cut into individual sized servings. Then the frozenportions are further dehydrated to a moisture content of about 2 percentby weight and packed in a moisture proof container. The bars ofnutritionally dense beef stew were reconstituted by pouring an excess of180° F. water over a food bar and permitting the bars to stand in thewater for a length of time as needed to substantially rehydrate the beefstew, this time amounting to about 2-3 minutes. The components of thebeef stew were similar in appearance and acceptance to that of the beefstew before molding.

Example 2

A chicken a la king food bar is prepared by mixing the followingingredients at the percentage levels noted:

    ______________________________________                                        Ingredient                %                                                   ______________________________________                                        Ground chicken, ground through 5/8 inch plate                                                           59.92                                               Mushroom stems and pieces 6.00                                                Frozen chicken broth      4.50                                                Frozen chicken fat        2.50                                                Slit frozen green peas    5.00                                                Mushroom brine            3.00                                                Powdered vegetable shortening                                                                           3.00                                                Canned diced pimentoes    3.00                                                Diced, dehydrated onions  1.50                                                Frozen green peppers      5.00                                                Monosodium Glutamate      0.64                                                Salt                      0.63                                                Ground celery             0.03                                                Lecithin                  0.38                                                White pepper              0.08                                                Ground bay leaf           0.04                                                Microcrystalline cellulose                                                                              0.75                                                Starch                    2.00                                                Gum arabic                2.00                                                Concentrated butter extract                                                                             0.06                                                ______________________________________                                    

This food bar is prepared by the same method described in Example 1. Thechicken a la king food bars had a density of 0.49g/cc, 82% of thedensity of similarly formulated compressed food bars. These food barshad significantly improved quality upon rehydration when compared to thecompressed food bars.

Example 3

A pork and escalloped potato food bar is prepared from the followingingredients:

    ______________________________________                                        Ingredient           %                                                        ______________________________________                                        Ground pork          53.05                                                    Dehydrated frozen potatoes                                                                         27.00                                                    Frozen diced green peppers                                                                         5.00                                                     Dehydrated meat stock                                                                              4.00                                                     Dehydrated cream cheese                                                                            3.50                                                     Dehydrated diced onions                                                                            2.00                                                     Gum arabic           2.00                                                     Corn starch, modified                                                                              2.00                                                     Salt                 1.00                                                     Lecithin             0.25                                                     Garlic powder        0.06                                                     Ground white pepper  0.03                                                     Ground celery seed   0.03                                                     Ground thyme         0.03                                                     Ground oregano       0.01                                                     ______________________________________                                    

This food bar is prepared by the same method described in Example 1. Thefood bar was of superior sensory quality after rehydration when comparedwith rehydrated compressed bars. The food bars had greater stabilitywhen stored at high temperatures than did compressed bars of similarformulation.

Example 4

A pork and rice oriental style food bar is prepared from the followingingredients:

    ______________________________________                                        Ingredient               %                                                    ______________________________________                                        Raw ground pork, ground with 5/8" blade                                                                54.30                                                Instant rice             26.00                                                Soy sauce                6.00                                                 Onion powder             1.50                                                 Ground corriander        0.25                                                 Garlic powder            0.10                                                 Ground celery seed       0.10                                                 Ground ginger            0.04                                                 Dehydrated meat stock    3.00                                                 Salt                     1.00                                                 Ground fennel            0.01                                                 Lecithin                 0.20                                                 Frozen slit green peas   2.50                                                 Cooked scrambled eggs    5.00                                                 Corn starch, modified    2.00                                                 Gum arabic               2.00                                                 ______________________________________                                    

The instant rice is cooked in water for about 3 minutes before beingadded. The pork and rice oriental food bars had densities of between0.60 and 0.64g/cc as compared to a density of 0.61g/cc for a freezedried compressed bar. This food is prepared according to the method ofExample 1.

EXAMPLE 5

A chicken stew food bar is prepared from the following ingredients:

    ______________________________________                                        Ingredient                %                                                   ______________________________________                                        Ground chicken, ground with 5/8" plate                                                                  43.31                                               Frozen chicken broth      6.00                                                Chicken fat               3.10                                                Diced Dehydrated onions   2.00                                                Salt                      1.00                                                Monosodium glutamate      0.28                                                White pepper              0.05                                                Ground celery seed        0.026                                               Ground bay leaf           0.023                                               Ground sage               0.023                                               Ground thyme              0.023                                               Ground all spice          0.01                                                Dehydrated frozen potatoes                                                                              19.50                                               Carrots (3/8 cubic inch)  13.50                                               Corn starch, modified     2.23                                                Dehydrated cream cheese   2.78                                                Lecithin                  0.28                                                Frozen slit peas          3.87                                                Gum arabic                2.00                                                ______________________________________                                    

The food bar is prepared according to the method of Example 1, producinga food bar of superior quality when compared to a chicken stewcompressed, dehydrated food bar.

Example 6

A spaghetti with meat sauce food bar is prepared according to the methodof Example 1 with the following ingredients:

    ______________________________________                                        Ingredient         %                                                          ______________________________________                                        Raw ground beef, 1/8" plate                                                                      58.55                                                      Tomato paste       19.00                                                      Salt               1.25                                                       Sugar              1.00                                                       Dehydrated chopped onions                                                                        1.00                                                       Dehydrated green peppers                                                                         1.00                                                       Oregano flakes     0.04                                                       Garlic powder      0.17                                                       Basil              0.04                                                       Cayenne pepper     0.03                                                       Ground bay leaf    0.02                                                       Parmesan cheese    2.00                                                       Ground fennel      0.01                                                       Ground thyme       0.01                                                       Ground celery seed 0.03                                                       Lecithin           0.25                                                       Dry 2 inch precut spaghetti                                                                      14.50                                                      Paprika            0.10                                                       Microcrystalline cellulose                                                                       1.00                                                       ______________________________________                                    

The spaghetti with meat sauce food bar had a density of 0.69g/cc, 112%the density of a similarly formulated freeze dehydrated compressed foodbar. The ground beef is cooked in excess water with all of the dryingredients except for the sphaghetti (which is cooked separately), thetomato paste and microcrystalline cellulose which are later added.

It is apparent from the above formulations that a wide variety ofvegetables, meat and meat vegetable combinations may be processed inaccordance with the present invention to produce nutritionally densefood items which are readily rehydratable. Other meats such as veal andlamb may be used as well as other vegetables. The process is much moreeconomical than prior processes which require compaction and multiplefreeze-vacuum dehydration steps. The food bars of this invention arevery storage stable when vacuum-packed in a moisture and gas-impermeablecontainer. As compared to those processes which required equilibrationof moisture prior to compression and those processes requiring twoseparate freeze-dehydration steps, the food items of this invention areless likely to experience oxidative rancidity during processing, thusreducing spoilage and deterioration in quality. The food bars of thisinvention rehydrate in 2 to 3 minutes with warm water (125°-200° F.)while many freeze dried compressed bars take 8 to 10 minutes or longerunder similar conditions. Some compressed bars will not rehydratecompletely no matter how long they remain in the water. The quality ofthe food bars was much better than compressed dehydrated bars,especially after storage for one month at 125° F. Much less rancidityand degradation were observed after this high temperature storage. Itwas found that food bars could be produced of a density approaching thatfound in bars compressed at high pressures. The spaghetti and meat saucefood bar had an even greater density than a compressed food bar.

It will be understood that various changes in the details of the processand the ingredients which have been herein described and illustrated inorder to explain the nature of the invention, may be made by thoseskilled in the art within the principle and scope of the invention. Forexample, any method of preconcentration (elimination of water) may beused such as vacuum evaporation, reverse osmosis, dialysis, etc.

We claim:
 1. A method of producing a nutritionally dense freeze driedfood bar comprising:a. preparing a mixture of uncooked food ingredientsof said bar, b. cooking and partially drying said mixture of uncookedfood ingredients until about 40% to about 60% of the water content isremoved by evaporation, c. forming the mixture into food bars, d.freezing said food bars, e. dehydrating said food bars to a moisturecontent which will produce a shelf-stable product, and f. packaging saidfood bars in a moisture and gas impermeable container.
 2. The method ofproducing a nutritionally dense freeze dried food bar according to claim1 wherein after dehydration the moisture content of said bar is fromabout 1 percent to about 5 percent by weight.
 3. The method of producinga nutritionally dense freeze dried food bar according to claim 2 wherein45-55 percent of said water content is removed during the cooking step.4. The method of producing a nutritionally dense freeze dried food baraccording to claim 3 wherein said bar is dehydrated to about 2 percentby weight moisture.
 5. A method of producing a nutritionally densefreeze dried food bar according to claim 4 wherein said cooked mixtureis formed into a bar by stuffing said mixture into a sausage casing. 6.The method of producing a nutritionally dense freeze dried food baraccording to claim 4 wherein said cooked mixture is formed into thedesired shape by packing in a mold.
 7. The method of producing anutritionally dense freeze dried food bar according to claim 5 whereinsaid food bar has a density between about 0.40 g/cc and about 0.70 g/cc.8. The method of producing a nutritionally dense food bar according toclaim 7 wherein said food bar has a density which is about 80% to about110% of the density of a second food bar which has been compressed atpressures above 300 pounds per square inch.
 9. The method of producing anutritionally dense freeze dried food bar according to claim 8 whereinsaid uncooked food ingredients, comprising the majority of the mass ofsaid food bar are selected from edible meats and vegetables, said meatsconsisting of chicken, beef, pork, lamb and veal and said vegetablesconsisting of potatoes, carrots, peas and onions.
 10. The method ofproducing a nutritionally dense freeze dired food bar according to clam9 wherein said uncooked food ingredients are selected from pork andrice; chicken, potatoes and carrots; ground beef and spaghetti; groundpork and potatoes; and ground beef, peas, carrots and potatoes.